U.S. patent application number 10/090713 was filed with the patent office on 2002-09-12 for high density optical source bank.
Invention is credited to Bennett, Steve, Minneman, Michael, Powers, John, Wood, Chris.
Application Number | 20020126274 10/090713 |
Document ID | / |
Family ID | 27376640 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020126274 |
Kind Code |
A1 |
Minneman, Michael ; et
al. |
September 12, 2002 |
High density optical source bank
Abstract
An optical test system for use in testing fiber optical
transmission systems and components comprises a modular
construction in a single housing. The modular construction includes
a plurality of laser source channels, a MUX, additional optical
conditioning devices both upstream and downstream of the MUX, and a
master controller for operating the system components in synchrony.
The integral housing, together with the modular construction,
provides increased structural density that occupies in many
instances at least seventy percent less space than is required for
other optical test systems. The use of a master controller to drive
the system affords expanded system functionality.
Inventors: |
Minneman, Michael;
(Broomfield, CO) ; Wood, Chris; (Boulder, CO)
; Bennett, Steve; (Broomfield, CO) ; Powers,
John; (Bozeman, MT) |
Correspondence
Address: |
LATHROP & GAGE LC
4845 PEARL EAST CIRCLE
SUITE 300
BOULDER
CO
80301
US
|
Family ID: |
27376640 |
Appl. No.: |
10/090713 |
Filed: |
March 1, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60273147 |
Mar 2, 2001 |
|
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|
60301993 |
Jun 29, 2001 |
|
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Current U.S.
Class: |
356/225 |
Current CPC
Class: |
G02B 6/428 20130101;
G02B 6/3817 20130101; G02B 6/266 20130101; H04B 10/079 20130101;
G02B 6/4274 20130101 |
Class at
Publication: |
356/225 |
International
Class: |
G01J 001/42 |
Claims
1. In an optical test system, the improvement comprising a housing
that contains at least eighteen laser source channels, and a master
controller internal to the housing operable for control of the
laser source channels, the master controller having a common
interface for commanding the laser source channels.
2. The optical test system of claim 1, comprising a volumetric
density of greater than 9.5 laser source channels per cubic
foot.
3. The optical test system of claim 1, comprising a vertical
density of at least 2.0 laser source channels per vertical inch in
a standard nineteen-inch-wide equipment rack.
4. The optical test system of claim 1, comprising at least forty
eight of the laser source channels internal to the housing.
5. The optical test system of claim 4, comprising a volumetric
density of greater than 9.5 laser source channels per cubic
foot.
6. The optical test system of claim 4, comprising a vertical
density of at least 2.2 laser source channels per vertical inch in
a standard nineteen-inch-wide equipment rack.
7. The optical test system of claim 1, comprising at least one
hundred of the laser source channels internal to the housing.
8. The optical test system of claim 7, comprising a volumetric
density of greater than 15 laser source channels per cubic
foot.
9. The optical test system of claim 7, comprising a vertical
density of at least 4.5 laser source channels per vertical inch in
a standard nineteen-inch-wide equipment rack.
10. The optical test system of claim 1, including a MUX located
internal to the housing.
11. The optical test system of claim 10, the MUX being configured
to produce a combined comb from the plurality of laser source
channels.
12. The optical test system of claim 11, including an optical
conditioning device internal to the housing in an optical pathway
downstream from the MUX, the optical conditioning device being
configured to provide optical processing on the combined comb.
13. The optical test system of claim 12, wherein the optical
conditioning device facilitates combining service channel WDM
signal processing with the combined comb.
14. The optical test system of claim 1, wherein the laser source
channel comprises a laser source card and a channel option
card.
15. The optical test system of claim 14, wherein the functionality
of the channel option card is selected from the group consisting of
a shutter, a variable optical attenuator, a polarization
controller, a polarization scrambler, a power monitor, and a
wavelength reference.
16. The optical test system of claim 15, wherein the channel option
card includes a laser power monitor configured to measure laser
power output from the laser source card.
17. The optical test system of claim 16, wherein the laser source
card includes a laser source and associated electronics integral to
the laser source card.
18. The optical test system of claim 17, wherein the laser power
monitor is configured to provide laser power measurement
information to the controller, the laser power measurement
information being representative of the total laser power output
from the laser source card including the laser source and the
associated electronics.
19. The optical test system of claim 18, wherein the master
controller is configured to adjust electrical power input to the
laser source card to control laser power output based upon the
power measurement information.
20. The optical test system of claim 1, including a modulation
controller internal to the housing configured for use in modulating
the laser source channels.
21. The optical test system of claim 20, where the modulation
controller is capable of generating a plurality of waveforms for
one of more channels.
22. The optical test system of claim 21, wherein the waveforms are
selected to include at least two members of the group consisting of
square waves, sawtooth waves, and sine waves.
23. The optical test system of claim 21, wherein the laser source
card is programmably configurable to operate a switch accepting a
selected one of the waveforms.
24. The optical test system of claim 23, wherein the laser source
card includes a gain block that is programmably configurable to
adjust an amplitude of the waveforms.
25. The optical test system of claim 24, wherein the gain block
operates by attenuating the amplitude of the waveform.
26. The optical test system of claim 1, wherein the master
controller is programmed with instructions comprising information
and command exchange protocols that include at least one protocol
selected from the group consisting of RS-232, GPIB, and
Ethernet.
27. The optical test system of claim 1, wherein the master
controller is operable for troubleshooting operations on the
optical test system.
28. The optical test system of claim 1, including an optical power
measurement module internal to the housing, the optical power
measurement module being configured to accept optical input from
external to the housing.
29. The optical test system of claim 1 including a data input
device capable of reprogramming the optical test system with
software upgrades.
30. The optical test system of claim 1, at least one of the laser
source channels comprising: a laser source card having a first
electrical connector operable for carrying electrical signals, and
a first optical coupling operable for carrying optical signals; and
a channel option card having a second electrical connector
compatible for mating engagement with the first electrical
connector to facilitate communication of the electrical signals to
the channel option card.
31. The optical test system of claim 30, wherein the housing
comprises a mounting system deploying the laser source card and the
channel option card sequentially.
32. The optical test system of claim 31, comprising a second
optical coupling compatible for mating engagement with the first
optical coupling to facilitate optical communication between the
laser source card and the channel option card.
33. The optical test system of claim 31, wherein the mounting
system includes a rail guide system for retaining the laser source
card and the channel option card in a straight line.
34. In an optical test system, the improvement comprising: a
housing that contains a plurality of laser source channels, and a
MUX located internal to the housing for use in combining signals
from the laser source channels.
35. The optical test system of claim 34, comprising a controller
located internal to the housing for use in modulating the laser
source channels.
36. The optical test system of claim 34, comprising at least
eighteen of the laser source channels
37. The optical test system of claim 34, comprising a volumetric
density of greater than 9.5 laser source channels per cubic
foot.
38. The optical test system of claim 34, comprising a vertical
density of at least 2.0 laser source channels per vertical inch in
a standard nineteen-inch-wide equipment rack.
39. The optical test system of claim 34, comprising at least forty
eight of the laser source channels internal to the housing.
40. The optical test system of claim 39, comprising a volumetric
density of greater than 9.5 laser source channels per cubic
foot.
41. The optical test system of claim 39, comprising a vertical
density of at least 2.2 laser source channels per vertical inch in
a standard nineteen-inch-wide equipment rack.
42. The optical test system of claim 34, comprising at least one
hundred of the laser source channels internal to the housing.
43. The optical test system of claim 42, comprising a volumetric
density of greater than 15 laser source channels per cubic
foot.
44. The optical test system of claim 42, comprising a vertical
density of at least 4.5 laser source channels per vertical inch in
a standard nineteen-inch-wide equipment rack.
45. The optical test system of claim 34, including an optical
conditioning device internal to the housing in an optical pathway
downstream from the MUX, the optical conditioning device being
configured to provide optical conditioning on the combined
comb.
46. The optical test system of claim 45, wherein the optical
conditioning device is selected from the group consisting of a
shutter, a variable optical attenuator, a polarization controller,
a polarization scrambler, a power monitor, and a wavelength
reference.
47. In an optical test system, the improvement comprising: a
housing that contains a plurality of laser source channels each
including a laser source card having a laser source; and a
modulation controller internal to the housing capable of generating
a plurality of waveforms for each laser source channel.
48. The optical test system of claim 47, wherein the waveforms are
selected to include at least two members of the group consisting of
square waves, sawtooth waves, and sine waves.
49. The optical test system of claim 47, wherein the laser source
card contains a programmably configurable switch for use in
accepting a selected one of the waveforms as drive input for the
laser source.
50. The optical test system of claim 47, wherein the laser source
card includes a gain block that is programmably configurable to
adjust an amplitude of the waveforms.
51. The optical test system of claim 50, wherein the gain block
operates by attenuating the amplitude of the waveform.
52. The optical test system of claim 51, wherein the laser source
card includes a bypass mechanism that is programmably configurable
to bypass the gain block.
53. The optical test system of claim 47, wherein the modulation
controller includes a plurality of waveform function output lines,
and a corresponding plurality of function generators allocated to
each of the waveform function output lines, each function generator
being capable of generating a generated waveform output on its
corresponding waveform function output line.
54. The optical test system of claim 53, wherein the modulation
controller includes a number of waveform input connectors allocated
to selected ones of the waveform function output lines, each
waveform input connector being capable of receiving waveform input
from an external function generator when an external function
generator is connected to the waveform input connector, and
providing the waveform input as output comprising an external
waveform output, and a corresponding number of programmably
configurable waveform selection switches capable of selecting
inputs between the generated waveform output and the external
waveform output, each of the corresponding number of switches being
allocated to one of the selected ones of the waveform input
lines.
55. The optical test system of claim 54, wherein each of the
selected ones of the waveform function output lines forms a shared
rail system coupled in common with each of the laser source
cards.
56. The optical test system of claim 55, wherein each of the laser
source cards includes a programmably configurable rail selection
switch capable of switching between the shared rail systems to
provide selected waveform outputs as drive input for the
corresponding laser source.
57. The optical test system of claim 56, wherein the modulation
controller includes a coherence rail system in communication with
each of the laser source cards, the coherence rail system including
a coherence control function generator capable of generating a
coherence control waveform output and a programmably controllable
coherence rail switch capable of selecting between the coherence
control waveform output and a ground.
58. The optical test system of claim 57, wherein the programmably
configurable rail selection switch in each laser source card is
capable of selecting between the coherence rail system and the
shared rail systems to provide drive input for the laser
source.
59. The optical test system of claim 47, wherein the modulation
controller includes a digital modulation rail system including a
digital modulation function generator capable of generating a
digital waveform output and a programmably controllable digital
modulation switch capable of selecting between the coherence
control waveform output and a ground.
60. The optical test system of claim 59, wherein each laser source
card includes a second switch capable of selecting between the
digital modulation rail system and ground.
61. The optical test system of claim 60, wherein the laser source
card includes a gain block for adjusting the amplitude of waveforms
from the shared rail system and the second switch provides a bypass
of the gain block.
62. The optical test system of any one of claims 1-61 produced by a
method including the steps of preconfiguring the optical test
system for use in test operations at a manufacturing facility prior
to shipping the optical test system to a customer.
63. A method of performing an optical test using an optical test
system having at least eighteen laser source channels, and a
controller, all in a single housing, the method comprising the
steps of: energizing the laser source channels to provide test
waveforms under control of the controller, and performing optical
test measurements through use of the test waveforms.
64. The method as set forth in claim 63, including a step of
operating the optical test system through use of a unified set of
program commands directed to the controller.
65. The method as set forth in claim 63 including a step of
executing software diagnostics through use of a telecommunications
linkage.
66. The method as set forth in claim 63 including a step of
combining the test waveforms into a combined comb through use of a
MUX located internal to the housing.
67. The method as set forth in claim 63 including a step of
operating the optical test system from a volumetric density of
greater than 9.5 cubic feet per laser source channel.
68. The method as set forth in claim 63 including a step of
operating the optical test system from a vertical density of at
least 2.0 laser source channels per vertical inch in a standard
nineteen-inch-wide equipment rack
69. The method as set forth in claim 63, wherein the optical test
system includes at least forty eight of the laser source channels
internal to the housing, and the method includes a step of
operating the optical test system from a volumetric density of
greater than 9.5 laser source channels per cubic foot.
70. The method as set forth in claim 63 wherein the optical test
system includes at least forty eight of the laser source channels
internal to the housing, and the method includes a step of
operating the optical test system from a vertical density of at
least 2.2 laser source channels per vertical inch in a standard
nineteen-inch-wide equipment rack.
71. The method as set forth in claim 63, wherein the optical test
system includes at least one hundred of the laser source channels
internal to the housing and the method includes a step of operating
the optical test system from a volumetric density of greater than
15 laser source channels per cubic foot.
72. The method as set forth in claim 63, wherein the optical test
system includes at least one hundred of the laser source channels
internal to the housing and the method includes a step of operating
the optical test system from a vertical density of at least 4.5
laser source channels per vertical inch in a standard
nineteen-inch-wide equipment rack
Description
RELATED APPLICATIONS
[0001] This application claims benefit of priority to U.S.
Provisional Application Serial No. 60/273,147, filed Mar. 2, 2001,
and U.S. Provisional Application Serial No. 60/301,993, filed Jun.
29, 2001, each of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of The Invention
[0003] The invention pertains to the field of optical source
equipment and related methods for use in fiber optic
communications. More specifically, the optical source equipment
includes an optical source bank that is used, for example, in
testing optical amplifiers and wavelength division multiplexing
(WDM) systems.
[0004] 2. Statement of the Problem
[0005] Rapid advances in WDM or dense wavelength multiplexing
(DWDM) provide cost-effective increases in the capacity of
fiber-optic data transmission systems through the use of multiple
wavelengths of light. DWDM is a highercapacity version of WDM. WDM
systems support the multiplexing of up to four channels or
wavelengths on a single fiber. Commercially available DWDM systems
support up to 40 wavelengths or channels, and this capacity is
steadily increasing. Data transmission capacity is also increased
by time division multiplexing (TDM) rates in which a plurality of
separate data signals are transmitted on the same line by
interleaving a piece of each signal one after another in time.
Maximum transmission capacity is determined as a trade-off between
the DWDM channel count and the maximum supported TE)M switching
rate. For example, a system operating on 40 channels at OC-48 with
TDM might operate at a net throughput of about 100 Gbps. Future
systems operating on the OC-192 protocol at 40 channels might have
a net throughput of 400 Gbps, and a future system operating on 100
channels might have a net throughput of one terabit per second.
[0006] While these future systems are not yet practical, continuing
advances in DWDM and TDM technology are expected to expand maximum
net throughput rates over the next several years.
[0007] The advances in net throughput rates require corresponding
advances in fiber-optic system components, which drive advances in
test components, test equipment and signal amplifiers. For example,
erbium-doped fiber amplifiers (EDFA) are used in DWDM systems to
eliminate or minimize the use of regenerative repeaters, and can be
used as in-line repeating amplifiers, transmitter booster
amplifiers, and receiver pre-amplifiers. EDFA devices comprise a
section of glass fiber, which is doped with erbium. The
erbium-doped fiber amplifies laser light transmitted through the
doped section of fiber. EDFA technology has been used, by way of
example, to support a mix of four 2.5 Gbps digital video streams in
delivery of an 80 channel AM cable television network signal over a
100 km distance using one EDFA at the output node and one at
midspan.
[0008] Optical test equipment for use in testing system components
for fiber-optic transmissions is continually outdated in the face
of rapid capacity advances. Traditional DWDM test equipment uses an
eight or sixteen channel multiplexer where, for example, eight
channels may be allocated to a mainframe. Attempts to provide
additional sources, e.g., more than 40 laser diodes that are each
linked with a corresponding channel, source modulation electronics,
attenuator, polarization control, and error injection devices
produce unwieldy agglomerated test systems that are connected with
a patchwork of optical cables. The test systems grow to occupy
large amounts of space, and test measurement errors may be induced,
for example, by movements in the optical cables that interconnect
the respective devices. Depreciation and use of optical test
equipment may comprise a substantial percentage, e.g., twenty or
thirty percent, of the total manufacturing costs of optical system
components.
[0009] A problematic side-effect of continually increasing capacity
in optical data transmission systems is that increased amounts of
space are required to accommodate the associated increases in
volume of test equipment. For example, such equipment is regularly
supported by racks. Each rack, according to industry standards,
typically has dimensions of approximately seventy-two inches in
height, twenty-seven inches in depth, and nineteen inches in width,
which corresponds to a rack volume of about 21.4 cubic feet.
[0010] To date, no manufacturer has been able to offer an optical
source array in the confines of a single integrated box containing
more than about seventeen laser sources within the box. Within
boxes formed to meet these restrictions the number of laser sources
are primarily limited by the size of the electronic and optical
assemblies required, and by heat dissipation requirements.
[0011] Many commercial systems do not use all of the available rack
space because, for example, the housing may be shallower or shorter
than the corresponding depth or height of the rack. One typical
system housing a total of eight laser source cards has dimensions
of five and one-quarter inches in height, seventeen and
three-quarters inches in width, and seventeen inches of depth, for
a total volume of 0.92 cubic feet. The eight laser sources or
channels in a single box of this volume produces a density of
approximately 8.7 laser sources per cubic foot inside the box, and
approximately 1.5 laser sources per vertical inch in the rack.
These numbers represent about the maximum density that can be
obtained within a single box due to the size of the electronic and
optical assemblies required, and to excessive heat dissipation from
electro-optical components in the box. The addition of special
cooling systems other than blowers for air convection systems is
practically not done because it adds significant cost and
maintenance complexity to these systems.
SOLUTION
[0012] The present invention overcomes the problems that are
outlined above by providing an improved optical test equipment
having modular components that reside in a single housing for a
dense system that occupies less rack space than prior systems and
is comprised of modular components that may be selectively and
programmably upgraded over time to accommodate increasing
throughput and bandwidth. These advantages are facilitated by a
densified way of coupling laser source cards with channel option
cards, together with use of improved theromolectric cooling systems
and laser pulse modulation systems.
[0013] Optical test systems produced in accordance with the
concepts described below may, for example, have exceptionally high
densities of laser source cards, all under the influence of a
master controller and a shared interface that is located internal
to the housing and operable for control of the laser source
channels. The master controller is compatible with information and
command exchange protocols for the transmission and receipt of
information. For example, the densities may exceed eight, ten,
twelve, fourteen, sixteen, eighteen, and even twenty sources per
cubic foot of space inside a single box.
[0014] The principles described herein may be applied to greatly
improve optical test system densities where, for example, specific
embodiments could include eighteen sources within a single housing
adapted to fit within a conventional test equipment rack to provide
a volumetric density of greater than 9.5 laser source channels per
cubic foot, and a vertical density of at least 2 laser source
channels per vertical inch in a standard equipment rack having a
width of nineteen inches. Another specific embodiment actually
constructed included an array of fifty channels internal to the
housing, to provide a volumetric density of greater than 9.5 laser
source channels per cubic foot and at least 2.2 laser sources per
vertical inch in a standard nineteen-inch-wide equipment rack. A
third specific embodiment actually constructed included one hundred
of the laser source channels internal to the housing to provide a
volumetric density of greater than 15 laser source channels per
cubic foot and a vertical density of at least 4.5 laser source
channels per vertical inch in a standard nineteen-inch-wide
equipment rack. These densities are unattainable in the prior art
and constitute a significant advance.
[0015] More than forty-eight, one-hundred, or even two hundred such
sources may be supported in a single equipment rack according to
the principles described herein, for example, one-hundred laser
source cards are housed on a standard test equipment rack in a
standard box having dimensions of twenty-one inches in height,
seventeen and three-quarters inches in width, and twenty-five and
one-half inches in depth.
[0016] The optical test system, according to one aspect of the
improvements described below, relates to a modular construction of
the individual channels, i.e., the system housing contains a
plurality of modular laser source channels. At least one of the
laser source channels includes a modular laser source card having a
first electrical bus and a first optical coupling. A modular
channel option card contains a second electrical bus that is
compatible for mating engagement with the first electrical bus and
a second optical coupling compatible for mating engagement with the
first optical coupling. A mounting system within the housing, such
as a rail guide, sequentially deploys the laser source card and the
channel option card to form a completed modular channel that may
assume any geometry, but is preferably oriented in a straight line
to optimize density of the channel array. There may be any number
of such channels provided in the array, such as 48, 100, or 200
such channels, which have heretofore not been controllable as a
single array.
[0017] The channel option card contains an optical conditioning
device, such as a shutter, a variable optical attenuator, a
polarization controller, a polarization scrambler, a power monitor,
and a wavelength reference device. These devices may be placed in
communication with a master controller for feedback and quality
control of optical test operations.
[0018] Additional optical conditioning devices may optionally be
provided within the same housing to provide further densification,
and all devices in the housing may be driven by a single master
controller to permit expanded test functionality and
synchronization. For example, a modular multiplexer (MUX) may be
located internal to the housing to provide a combined comb of laser
wavelengths from the channel array. Additional modular optical
conditioning devices or components may be placed internal to the
housing in an optical pathway downstream from the MUX to provide
optical conditioning on the combined comb. The functionality of the
additional optical conditioning devices downstream of the MUX may
be the same as or different from that of the functionality of the
channel-specific optical conditioning device on the channel option
card. In addition, the downstream devices may include other
options, such as service channel WDM signal processing relating to
the combined comb.
[0019] In a particularly preferred option, the channel option card
includes a laser power monitor that is configured to measure laser
power output from the laser source card. The laser power monitor is
configured to provide laser power measurement information to the
controller, where the laser power measurement information
represents the total laser power output from the laser source card
including a laser source and associated electronics and optics. The
controller is configured to adjust electrical power input to the
laser source card and control laser power output based upon the
power measurement information. This technique differs from prior
systems that adjust laser power input based upon gain at the laser
chip alone, and ignore the effects of other electronics and optics
on the laser source card.
[0020] A further aspect of the optical test system, according to
preferred instrumentalities of the invention, includes the
provision of optical connectors configured to provide laser source
input to the plurality of channels when the optical connectors are
coupled with an external laser source. A plurality of such systems
can be coupled to multiply the total number of channels that are
combined in a single MUX; this permits, for example, two of such
systems to be coupled in a manner that doubles the number of
channels passing through the MUX of the second system Yet another
aspect of the optical test system, according to preferred
instrumentalities, includes the provision of a programmable
modulation controller that resides within the same housing and is
capable of generating a plurality of waveforms. The modulation
controller includes a plurality of function generators that, for
example, generate waveforms including at least two members of the
group consisting of square waves, sawtooth waves, and sine waves.
In particularly preferred instances, the modulation controller
discharges these waveforms into a shared rail system connected to
each channel. The laser source card in each channel is programmably
configurable to operate a switch accepting a selected one of the
waveforms from the rail system. The laser source card may include a
gain block that is programmably configurable to adjust an amplitude
of the selected waveform, e.g., by attenuation or amplification,
and additional switching mechanisms in the laser source card may
selectively bypass the gain block.
[0021] It is especially preferred that the master controller be
compatible with information and command exchange protocols for the
transmission and receipt of information to and from external test
system components. By way of example, these protocols may include
at least one protocol selected form the group consisting of RS-232,
GPIB, Ethernet, and telephony networking protocols (e.g., for modem
dial-up connections). By way of example, a modem networking
protocol may be used for troubleshooting operations on the optical
test system.
[0022] While the concepts of the optical test system that are
described above emphasize the importance of providing modular
system components in a single, compact, and dense housing, it is
also permitted to connect the optical test system with other
devices that are external to the system, and these external devices
may even include additional optical test components or network
controllers. For example, an optical power measurement module
internal to the housing may be configured to accept optical input
from test system components external to the housing. The transfer
of information between the internal and external systems may be
governed by a network controller.
[0023] Other aspects of the optical test system, according to
preferred instrumentalities, include the provision of a data input
device, such as a disk drive or Internet connection, that is
capable of reprogramming the optical test system with factory
software upgrades.
[0024] In preferred embodiments, the aforementioned modulation
controller of the optical test system is programmably configured
for mutual interaction with the laser source card. The laser source
card contains a programmable configurable switch for use in
accepting a selected one of the waveforms as drive input for the
laser source.
[0025] In especially preferred embodiments, the modulation
controller includes a plurality of waveform function output lines,
and a corresponding plurality of function generators allocated to
each of the waveform function output lines. Each function generator
is capable of generating a waveform output on its corresponding
waveform function output line. A number of waveform input
connectors are allocated to selected ones of the waveform function
output lines. Each waveform input connector is capable of receiving
waveform input from an external function generator when an external
function generator is connected to the waveform input connector.
Each waveform input connector is also capable of providing the
waveform input as output comprising an external waveform output. A
corresponding number of programmably configurable waveform
selection switches in the modulation controller are capable of
selecting inputs between the generated waveform output and the
external waveform output. Each switch of the corresponding number
of switches is allocated to one of the selected ones of the
waveform input lines, which preferably and collectively form a
shared rail system coupled in common with each of the laser source
cards.
[0026] To provide compatible interaction between the laser source
card and the modulation controller in these especially preferred
embodiments, each of the laser source cards includes a programmably
configurable rail selection switch capable of switching between the
shared rail systems to provide selected waveform outputs as drive
input for the corresponding laser source.
[0027] The modulation controller may include additional rail
systems, such as a coherence rail system in communication with each
of the laser source cards. The coherence rail system includes a
coherence control function generator capable of generating a
coherence control waveform output and a programmably controllable
coherence rail switch capable of selecting between the coherence
control waveform output and a ground. Accordingly, the programmably
configurable rail selection switch in each laser source card is
capable of selecting between the coherence rail system and the
shared rail systems to provide drive input for the laser
source.
[0028] Another rail system that the modulation controller
optionally provides may comprise a digital modulation rail system
including a digital modulation function generator capable of
generating a digital waveform output, and a programmably
controllable digital modulation switch capable of selecting between
the coherence control waveform output and a ground. In this case,
each laser source card may include a second switch that is capable
of selecting between the digital modulation rail system and a
ground. The second switch on the laser source card may provide a
bypass of the gain block that feeds the digital waveform output
directly to the laser source.
[0029] A particular advantage of the modular construction that is
described above is that it enables methods of manufacture and use
that are not enabled by prior systems. For example, the optical
test system may be produced by a method including the steps of
preconfiguring the optical test system for use in test operations
at a manufacturing facility prior to shipping the optical test
system to a customer. The optical test system is fully ready for
the performance of test operations when the customer receives the
optical test system as an integrated package.
[0030] The method of making the optical test system may, for
example, comprise the steps of inserting into the housing a
plurality of modular laser source channels, that include a laser
source card having a first electrical bus and a first optical
coupling, and placing into the housing a modular MUX in
communication with each laser source channel. Additional steps may
include inserting a modular optical conditioning device internal to
the housing in an optical pathway downstream from the MUX, and
programmably configuring the optical conditioning device for
integrated system use as a device selected from the group
consisting of a shutter, a variable optical attenuator, a
polarization controller, a polarization scrambler, a power monitor,
and a wavelength reference device. Where the optical test system
includes a master controller internal to the housing, the step of
programmably configuring may include a step of programmably
configuring the master controller. Furthermore, the method may
include adding a modular channel option card, or an array of such
cards, to the laser source channel. The system may be calibrated at
the manufacturing facility, and it may be constructed by specially
trained technicians to incorporate all of the requirements of a
complete test system using materials, such as special laser diodes,
that are either provided by or specified by the customer. This type
of special construction greatly reduces setup downtime upon arrival
of the completed test system. Similarly, the integrated modular
optical test system permits greater system accuracy and control of
expanded test operations according to a method of optical testing.
Where, for example, the optical test systems includes a plurality
of laser source channels, a MUX, additional optical components, and
a master controller all confined in a single housing, a method of
use may include energizing the laser source channels to provide
test waveforms, and combining the waveforms through use of the MUX
to provide a combined comb. The method of use may further include a
step of operating the optical test system through use of a unified
set of program commands directed from the master controller.
Additionally, the method may include a step of trouble-shooting
system problems through use of a telecommunications linkage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a schematic block diagram depicting an integrated
modular optical test system that includes a modular laser source
channel array and internal MUX that operate according to the
principles described above;
[0032] FIG. 2 depicts an optional channel configuration for the
optical test system, wherein a fiber bundle provides input to the
MUX;
[0033] FIG. 3 depicts another optional channel configuration for
the optical test system, wherein an optical fiber bypasses the
MUX;
[0034] FIG. 4 depicts yet another optional channel configuration
for the optical test system, wherein a laser source card couples
with a corresponding optical coupling and an electrical bus;
[0035] FIG. 5 is a circuit schematic depicting a modulation
controller and connections to an array of laser source cards that
are used for waveform switching operations that provide selected
waveforms to drive a plurality of laser sources from a common rail
system;
[0036] FIG. 6 is a process flow diagram illustrating a method of
making the optical test system; and
[0037] FIG. 7 is a block functional diagram illustrating aspects of
firmware that are used to program the optical test system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0038] FIG. 1 is a schematic block diagram of an optical test
system 100 illustrating, by way of example, a modular structure
that operates according to preferred principles of the
invention.
[0039] An optical source array 102 is comprised of a plurality of
individual channels, such as channel 103, which each contain a
corresponding plurality of elements. The optical source array
contains a total of N such channels, where N may be, for example,
100 or 200 channels as needed for test purposes. The optical source
array, as depicted in FIG. 1, consumes less power and occupies a
smaller footprint than prior devices. An additional advantage is
that the array may be selectively configured to meet the demands of
specific test purposes and need not be provided with too many
channels. Additional channels may be selectively added or removed
to meet future demands.
[0040] The individual channels of the optical source array 102 are
modularly constructed to meet the needs of specific test
situations. By way of example, in the optical source array 102, a
laser source module bank 104 includes a plurality of individual
laser source module cards, e.g., card 106 including a laser diode
or any other type of optical telecommunications laser source. An
example of a commercially available laser source module is the 515
module available from ILX Lightwave of Boulder, Colo. A modulation
switch circuitry bank 108, e.g., comprising individual switch
circuitry 110, permits selective laser modulation according to
permitted system modulation functions, such as sine wave, square
wave, triangular or sawtooth wave, and rectangular wave function
modulations, for each laser source module card as will be described
in more detail below. A thermal pulse modulation control bank 112,
e.g., formed of thermoelectric cooler/heater (TEC) circuitry 114,
compensates for temperature variances in the individual laser
diodes of the laser source module array 104 to provide a stable
laser output. In each channel, the laser source module cards, such
as card 106, preferably include the switch circuitry 110 and the
TEC circuitry 114 as integral components; however, the switch
circuitry 1 10 and the TEC circuitry 114 may be provided as
separate modular cards with compatible plug-in connectors.
[0041] A channel option array 116 comprising individual channel
option cards, such as card 118, may be selectively added using
commercially available components to provide shutter control for
each laser, a variable optical attenuator, a polarization
controller a polarization scrambler, a power monitor, and a
wavelength reference. These devices may be used individually,
selectively combined in series, or not used at all, depending upon
test needs.
[0042] In cases where the channel option card 118 is a power
monitor card, it is preferred to use a tap coupler, e.g., a 99%/1%
coupler where power measurement is made on the 1% tap. Prior power
monitor devices monitor current at a laser chip on the laser source
card and use this measurement to stabilize the power output of the
laser. Prior techniques are, therefore, only sensitive to effects
on the laser that can affect the power stability. These techniques
are insensitive to power changes that derive from changes in the
other optical and circuitry elements that are connected to the
laser. Placing a power monitor downstream of the laser in the
position of card 118 advantageously permits monitoring and/or
selective adjustment of laser power output based upon the total
channel laser power output.
[0043] Where, for example, the channel option card 118 is a
polarization controller or polarization scrambler, the card
operates upon polarized light from the laser source card 106 to
align polarization in a controlled manner to optimize external
modulation power and to control polarization dependent dispersion
and polarization-dependent loss. A polarization scrambler generates
all states of polarization in a certain time interval, which
averages out polarization-dependent effects. By way of example, a
commercially available device that can be used as both a
polarization alignment device and a polarization scrambler is, by
way of example, the Polarite II model PCS-3X-PC/APC-7 which is
available from General Photonics.
[0044] Where, for example, the channel option card 118 is a
wavelength reference, or wavelength lock an optical filter and
power meter provide feedback that measure and stabilize the laser
frequency from the laser source card 106. The feedback signal is
derived using the intensity or phase of light that is reflected
from or transmitted through the filter.
[0045] Where, for example, the channel option card 118 is a
shutter, the shutter mechanism, such as a mechanically actuated
fiber switch in a V-groove mount, is preferably used to disrupt or
transmit laser emissions from the laser source card 106 without
having to change the current at the laser. This ability avoids the
necessity of deenergizing and reenergizing the laser, which
requires a long settling time to stabilize laser emissions upon
reenergization. By way of example, commercially available shutter
devices include the model FOSW 1-1-L-PC-L-1 shutter from
ChynOptics, which has a 50 ms switching time.
[0046] Where, for example, the channel option card 118 is a
variable optical attenuator, such as the OZ Optics model
DD-100-11-1550-9/125-S-40- -3D3S-1-0.5--485:1-6-MC/SPI, the
attenuator is used to reduce the intensity of light in the channel
103 to much lower and stable power levels than the laser source
card 106 can achieve alone with a reduction in current. The
individual channel attenuator reduces the power level of the
channel for whatever level is needed for the combined comb using
one device before the comb is delivered to a system under test.
[0047] Each channel in the optical source array 102 shares a common
electrical backplane 120 and a common optical backplane 122, which
respectively provide compatible electrical or optical couplings
that mate with corresponding couplings on the individual channels.
The specific manner of connectivity is not critical, so long as the
connectors provide the optical and electrical pathways that are
required for module compatibility with the optical test system
100.
[0048] An optional but preferred multiplexer (MUX) 124 combines the
individual channel emissions from the optical source array 102 to
provide a combined comb including the combined emissions. For
example, a commercially available MUX is the model
AWG-NG-48x1-100G-1.5--FC/APC from SDL PIRI. The creation of a
wavelength comb within a single instrument advantageously
facilitates operations on the combined comb within the test system
100, as opposed to prior techniques requiring a separate device
that occupies an additional footprint. Comb operations are,
accordingly, simplified and expanded, as a single programmable
controller is enabled to direct these functions in a more versatile
manner than could be obtained from separate devices. An additional
advantage is that fiber management and integrity is controlled
within the enclosure of test system 100, which reduces set-up time
and the risk of fiber damage.
[0049] The optical pathway proceeds from the multiplexer 124 to a
series of optional modular service channel WDM processors 126 and
128, which are coupled with corresponding service channel sources
130 and 132 for conventional data transmission signal processing,
e.g., for WDM-TDM handshake recognition relating to endpoint
interpretation of the channels in the combined comb.
[0050] A beam splitter 134, e.g., a 99%/1% splitter, provides light
from the combined comb to an auto-calibration device 136, which
includes an optical filter and power meter that provide feedback
for measurement and stabilization of the laser frequency. The
feedback signal is derived using the intensity or phase of light
that is reflected from or transmitted through the filter at
emission wavelengths corresponding to the design wavelengths for
the channels of laser source array 104. Power control of individual
laser source cards in the laser source array 104 may, thus, be
regulated after MUX processing to form a combined comb.
[0051] An optional variable optical attenuator 138, such as the OZ
Optics model DD-100-11-1550-9/125-S-40-3D3S-1-0.5-485:1-6-MC/SPI,
reduces the intensity of light in the combined comb downstream of
MUX 124 to much lower and stable power levels than the laser source
array 104 can achieve alone with a reduction in laser diode
current. The individual channel attenuator reduces the power level
of the channel for whatever level is needed for the combined comb
using one device before the comb is delivered to a system under
test.
[0052] A polarization controller or polarization scrambler 140
operates upon the combined comb downstream of MUX 124 to align
polarization in a controlled manner to optimize external modulation
power and to control polarization dependent dispersion and
polarization-dependent loss. A polarization scrambler generates all
states of polarization in a certain time interval, which averages
out polarization-dependent effects and identifies minimum and
maximum transmission orientations. By way of example, a
commercially available device that can be used as both a
polarization alignment device and a polarization scrambler is the
Polarite II model PCS-3X-PC/APC-7, which is available from General
Photonics.
[0053] A splitter 142 divides the optical pathway for the combined
comb into a polarized output segment leading to polarizer 144 and a
non-polarized segment 146. The segment leading to polarizer 144 is
in optical communication with an optical power measurement module
148, which monitors the power output in the combined comb at
different polarization states. Optical connectors 150 and 152 are
present to receive optical input from other sources external to the
optical test system 100, such as a system power monitor 154 or a
general-purpose power monitor 156.
[0054] The non-polarized segment 146 is advanced by a splitter 158
or a series of such splitters leading to an output panel 160
including a plurality of optical connectors 162 and 164. The panel
160 may be provided on the front or rear of the optical test system
100, or two or more such panels 160 may be present on both the
front and rear or the sides.
[0055] The foregoing discussion has focused primarily upon the
optical pathway within the optical test system 100, and the
discussion of electronics has until now not included a discussion
of the control circuitry. A master control circuit 166 includes a
central processing unit, magnetic or optical data storage, random
access memory, and program logic, as required to interact with
other system components of the optical test system 100 during
normal system control operations in the intended environment of
use. For example, the master control circuit 166 may comprise a
conventional motherboard for a personal computer, as well as any
other circuitry and data storage devices that are commonly used
with computers. A modulation control module 168 is provided to
drive laser source emissions from the laser source array 106
according to standard test practices. The modulation control module
168 may also be incorporated as part of the master control circuit
166. The modulation control module 168 is provided with a plurality
of N connectors, such as connector 170, for use in coupling with an
external modulation input source 172. These connectors may be
optical or electrical connectors, and the number of connectors
corresponds to the number of waveform modulation options in the
optical source array 102. Thus, the external modulation input
source 172 may be configured to drive modulation of the optical
source array 102 in a manner that is not provided for by the
electronics in the modulation control module 168.
[0056] The electronics on modulation control module 168 include a
function generator that accepts instructions from the master
control circuit 166 to drive individual elements (e.g., laser
source card 106) of the laser source bank 104 in a predetermined
manner that is compatible with conventional test practices. This
function generator may be switched to an OFF mode to accept
external inputs.
[0057] In an ON mode, the function generator provides sine waves,
triangular or sawtooth waves, square waves, and any other wave form
that is known or useful to those skilled in the art. The modulation
depths are selectively adjustable from 0 to 100%. The modulation
control module preferably provides signals comprising a plurality
of these waveforms to each channel in the optical source array 102,
and individual channels are intelligent in the sense that they are
programmed by instructions from the master control circuit 166 to
accept one of the provided waveforms to energize the laser.
[0058] An optical or magnetic disk drive 174, such as a Zip drive,
is used to provide software upgrades to the master control circuit
166, as well as to log the performance of optical test system 100.
These functions may also be accomplished using a modem or network
connection to an appropriate server, e.g., an Internet server, or
other suitable terminus.
[0059] A front panel display 176, e.g., a 10-inch color liquid
crystal display or plasma display panel, provides a graphical user
interface showing all of the source channels in the optical source
array 102, their emission power levels, and the emission
wavelengths. An intuitive command set is provided for interaction
with the master control circuit 166 to allow rapid modifications to
the system setup. Single source commands are provided to adjust the
properties of individual lasers on each channel. Comb commands are
provided to adjust the properties of the complete comb. Modulation
functions are provided to adjust the operation of the modulation
control module 168.
[0060] The optical test system is compliant with any number of data
transmission protocols that are commonly used in networking and
optical test systems. External interfaces 178 exist for connections
to other devices that use these protocols, such as RS-232, GPIB,
and Ethernet. Furthermore, these interfaces preferably include a
modem connection for either an internal or external modem, which
interfaces with the manufacturer of optical test system 100 for
trouble shooting purposes. The modem may also provide real-time
test measurement data summaries to remote locations or a telephony
network.
[0061] Except for those components that are specifically noted
above as being external to the optical test system 100, all of the
system components that are described above are preferably internal
to a single box 180, and are provided as modular cards or boards
that may easily be replaced or renewed on a component by component
basis. This feature provides an extremely compact modular system
that occupies a small footprint and can be upgraded for small
incremental costs over a period of many years.
[0062] External optical and electrical systems can also be provided
for use in combination with the optical test system 100. For
example, each channel in the optical source array 102 is preferably
provided with an optical connector, such as connector 182, that
accepts a fiber optic coupling for connection with an additional
optical source system, such as an external microwave modulation
system 184, which may, for example, be an optical test mainframe.
In this manner, additional sources may be combined into the comb
that is processed through MUX 124.
[0063] Similarly, external optical devices may be provided
downstream of the optical test system 100, e.g., a generic device
186, with power measurements being obtainable at any point from the
downstream pathway by a simple tap, such as tap 188, for feedback
to the optical power measurement module 148 through one of
connectors 150 or 152. Further splitters, such as 2.times.2
splitter 190 and 1.times.1 splitter 192 may be used as needed to
branch the optical pathway to other equipment 194, which may
include measurement systems such as power meters and the like, or
it may branch to open system architecture or networks. Other
pathway branches, for example, lead to test equipment, which may
include 1.times.N switches for the testing of, for example, erbium
doped fiber amplifiers (EDFA) or other DWDM system components.
[0064] FIGS. 2-4 provide additional detail concerning optional
configurations for use of the individual channels, e.g., channel
103, of the optical source array 102 In FIGS. 2-4, like numbering
has been retained with respect to identical elements that are shown
in the FIG. 1 schematic diagram, however, the configurations differ
in a user-determined manner.
[0065] FIG. 2 depicts the optical source array being fed by a laser
source channel 103. A first pathway segment 202 within channel 103
feeds laser output to optical coupling 182, which resides in the
electrical/optical backplane 122. In turn, a second fiber optic
cable 204 feeds MUX 124, which also accepts a fiber optic bundle
206 to provide a combined comb output to fiber optic cable 208. In
turn, fiber optic cable 208 feeds optical coupler 162 in the output
panel array 160. In this embodiment, the optical elements 126
through 158 are not required and may be either absent in optical
test system 100 or bypassed by a patch cable. The pathway segment
202 may include one or more channel option cards, such as a
shutter, variable optical attenuator, polarization controller,
polarization scrambler, power monitor or wavelength reference card,
as described in the context of channel option bank 118 in FIG.
1.
[0066] FIG. 3 shows a configuration that is identical with respect
to FIG. 2, except the MUX 124 is absent in FIG. 3. A bypass cable
300 travels directly to the connector 162 in the output panel array
160.
[0067] FIG. 4 depicts insertion of a laser source module card 106
into channel 103 The laser source module card 106 contains a
printed circuit board 400, which has compatible electronics for
modulation of a laser source 402, such as a laser diode 404, which
is coupled with fiber optic cable 406 leading to a plug-in optical
connector 408. The printed circuit board 400 also has an electrical
bus 410, such as a PCI bus. The optical coupler 408 and the bus 410
mate with corresponding receptacles 412 and 414 in the
electrical/optical backplane 122 for the transmission of electrical
and optical signals. The channel option cards (not depicted in FIG.
4), such as channel option card 118 shown in FIG. 1, may be
daisy-chained with the laser source card 106 by opposite pairs of
electrical buses and optical connectors that are identical to the
optical coupler 408, the bus 410, and receptacles 412 and 414
[0068] FIG. 5 is a circuit diagram that schematically depicts
switching logic in the electronics of the modulation control module
168 and a plurality of laser source module cards, such as card 106,
which are denoted in FIG. 5 as cards 106A, 106B, and 106C.
[0069] Within the modulation control module 168, there exist a
plurality of function generators 500, 502, 504, and 506. The
function generators 500 and 502 are program configurable to
generate any type of waveform, such as a sine, square, or
triangular waveform, that may be useful in the optical test system
100. The function generators 500 and 502 are normally programmed to
generate signals that differ from one another as, for example, sine
waves and square waves. Function generator 504 provides what is
commonly known as a coherence control sine wave, which creates a 1
GHz line width in the laser emission. Function generator 506 is a
digital function generator that switches between full on and full
off. The amplitude of signal modulation provided from the
respective function generators is +/-1V for a peak-to-peak
amplitude of 2V. A number of external source inputs from the
external source input array 170 (see FIG. 1) provide an option for
bypassing the function generators 500-506, except the function
generator 504 does not necessarily need a bypass. Thus,
programmably controlled switches 514, 516 and 518 permit a user to
configure each channel of the optical source array 102 (see FIG. 1)
for use with an integral function generator or an external waveform
source. The coherence control signal may be turned on or off by
switching to ground. A digital modulation output jack 520 is
provided to permit synchronization of signal timing between
multiple interconnected optical test systems 100.
[0070] Output from the various waveform sources travels on
dedicated lines or rails, such as line 522 for modulation 1, line
524 for modulation 2, line 526 for coherence, and 528 for TTL
digital switching. Each of laser source cards 106A to 106C is
connected to the lines 522-528 in an identical manner, which is
described herein in reference to card 106A. A programmably
controlled switch contains three terminals 532, 534 and 536, which
are respectively connected to corresponding lines 522, 524 and 526.
A switching terminal is selectively connected to one of the three
terminals 532-536 for modulation of a laser diode 540 according to
the waveform on the corresponding one of lines 522-526. As shown in
the case of card 106A, this connection is between terminal 536 and
line 526. A programmably controlled gain block 542 is used to
attenuate the amplitude of the waveform to a peak-to-peak value
less than the 2V peak-to peak value on the corresponding one of
lines 522-526. A second switch 544 is used to modulate the laser
diode 540 at full amplitude using digital switching with bypass of
the gain block 542. As shown in the case of card 106A, switch 544
is set to enable digital switching. Alternatively, switch 544 could
be switched to ground, in which case modulation from terminal 536
and line 526 would be enabled.
[0071] FIG. 6 depicts a flow chart that represents the various
setup configuration options for optical test system 100. Except as
noted below, this setup is performed at the factory prior to
delivery of the optical test system 100 to the customer. In step
600, the system is provided as an empty box that requires various
modules to be installed according to a customer's test needs. A
decision is made in step 602 as to the source of laser diodes for
the laser source bank 106. This decision has three options. The
customer can supply precalibrated diodes for factory installation
in step 606. The factory can install a recommended array, e.g., for
specific DWDM test applications, in step 606, or nothing is
installed so that the customer can install the diodes in step
608.
[0072] A decision is made in step 610 whether to install a small
signal modulation option. If yes, then in step 612 a modulation
control module 168 is installed that permits modulation to signal
depths ranging from 0 to 100%. If no, the modulation control module
168 is installed without this option. These options may be provided
as an add-on board or chip in a standard modulation control module.
Similarly, a decision is made in step 614 whether to install a
large signal modulation and coherence control option. If yes, then
a modulation control module 168 is installed in step 616 with these
options enabled. If no, the modulation control module 168 is
installed without this option.
[0073] A decision is made in step 618 whether polarization control
should be installed. If yes, then channel option card, such as card
118, is installed to provide this function in step 620.
[0074] This process is repeated for all of the optional modular
system components that are shown in FIG. 1. For example, a decision
is made in step 622 whether a source shutter will be installed as
one of the channel options for card 118. If yes, then the shutter
option card is added to one or more channels of the optical source
array 102 in step 624. This pattern may be repeated for the MUX
124, as well as the optical system components 128 through 158,
according to customer specifications. Accordingly, it is seen that
the modularity of optical test system 100 permits factory setup and
calibration in a manner that could not be obtained from prior test
systems, which typically are assembled at the test site by the
customer and may include components from different manufacturers
that may have numerous incompatibilities. The factory setup also
eliminates test measurement errors due to erroneous, poor or
non-optimized installation of system components, and the inclusion
of modules within a single system permits on-line factory
diagnostics through use of a modem in the external interfaces 178.
Furthermore, soft patches for system upgrades and new drivers may
be added to the modular system through use of the data storage
drive 174.
[0075] FIG. 7 depicts a block diagram of preferred firmware
functionality within optical test system 100. This functionality is
executed by program instructions in the master control circuit 166.
Block 702 lists various input/output functions. The system accepts
outside commands and functions, for example, as directed by a
controller for the external microwave modulation source for
synchronization of the optical source array 102. Block 702
maintains a display on the front panel display 176 denoting the
current comb or pipeline status for each channel. Block 702 also
interprets or fields keystrokes from the front-panel display and
updates the display according to these keystrokes. Block 702 also
controls the GPIB controller, e.g., a TNT 4882 controller, and the
RS 232 transceiver, as described in connection with the external
interfaces 178. Block 702 also parses SCPI commands from a host
computer, which may be part of the master control circuit 166 or a
remote processor on a network. Block 702 also maintains the current
data structure of the optical test system 100.
[0076] Block 704 represents source and measurement functionality.
Block 704 interprets tokenized commands that are passed from block
702 by translating these commands into corresponding source code
and measurement commands. Block 704 manages the status of the laser
sources in each channel of the optical source array 102. Block 704
also creates and controls a measurement module wherein the output
of the respective channels may be coordinated with measurements
obtained from the channel output, such as power measurements
obtained from the channel option bank 116 or test measurements
obtained from the test equipment 196 when such measurements can be
allocated back to a particular channel or source. Block 704
additionally controls other devices in the optical pathway of
optical test system 100, such as polarization controllers or
scramblers. Block 704 maintains the data structure of each channel,
as needed for channel configuration and passes instrument
configuration information to block 702.
[0077] Block 706 pertains to control functions for the laser source
cards, such as card 106, which each may be provided with their own
processor. Block 706 interacts with block 704 by receiving
byte-level source code and transmitting source status information.
Block 706 uses the byte-level source to control energization of the
individual laser diodes or DFB's. Block 706 set the power and
wavelength of the laser emission according to limits that are
within predetermined system specifications. Block 706 maintains
calibration tables for each laser source, and it drives a
source-level polarization controller, as will be explained in more
detail below.
[0078] Block 708 pertains to measurement processor functions, which
may include calibrated optical power measurements at system taps,
such as may be measured through the optical power measurement
module 148 or the channel option bank 116. Block 708 controls the
MUX 124, which may from time to time require servo adjustment of
optical components in the case of a tunable MUX. Block 708
maintains calibration tables for photodiodes that are used in
obtaining optical measurements. Block 708 autoranges and adjusts
measurements for a chosen photodiode.
[0079] Due to the densification of the channel source array 102, as
made possible by the concepts discussed above, temperatures within
the housing may rise in comparison with respect to less dense
sources. The increased temperatures are associated with temperature
dependant effects upon the system electronics. These effects could
ostensibly result in test measurement variances unless the system
electronics accommodate these variances. Accordingly, a new method
of cooling the laser diodes has been devised, which includes a
switch-mode bi-directional control of laser diode temperature.
[0080] The circuitry is preferably located in the laser source
cards, such as laser source card 106, and includes a thermoelectric
cooler/heater device having a Peltier junction between a first
junction conductor and a second junction conductor. A switch-mode
DC power supply is electrically connected to the first junction
conductor and the second junction conductor for flowing DC
electrical current across the Peltier junction. The Peltier
junction operates as a heater when current flows in one direction
and a cooler when current flows; in the other direction. The
thermoelectric controller is heat-conductively connected to the
laser diode on the laser source card. The master controller 166 or
other control logic integral to the laser source card uses
measurements from a temperature sensor to switch the DC current
direction in maintaining the temperature of the laser diode within
a preferred operating range. Additional information concerning the
thermoelectronic controller may be found in provisional application
serial No. 60/272997 filed as a provisional application on Mar. 2,
2001, which is hereby incorporated by reference to the same extent
as though fully repeated herein.
[0081] The foregoing discussion is intended to illustrate the
concepts of the invention by way of example with emphasis upon the
preferred embodiments and instrumentalities. Accordingly, the
disclosed embodiments and instrumentalities are not exhaustive of
all options or mannerisms for practicing the disclosed principles
of the invention. The inventors hereby state their intention to
rely upon the Doctrine of Equivalents in protecting the full scope
and spirit of the invention.
* * * * *